The Kote Gaeshi wristlock is one of the first locks I learned in Traditional JJ. For those not familiar, it is the compressing and twisting lock where your thumb(s) is on the back of their hand with your gripping fingers at the base of their wrist.

The lock occurs as you rotate their own wrist up and inward. It becomes a throw when foot work is added as the lock has a way of pulling them out of balance.

Of course, for SD the throw is more of a crumple as without proper ukemi, the uke just gets his wrist broken.